<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="text" id="i1">
<input type="text" id="i2">
<input type="button" value="加" onclick="f(1)">
<input type="button" value="减" onclick="f(2)">
<input type="button" value="乘" onclick="f(3)">
<input type="button" value="除" onclick="f(4)">
<h3>
    结果:<span></span>
</h3>
<script>
    let a=document.querySelector("#i1");
    let b=document.querySelector("#i2");
    let s=document.querySelector("span");
    function f(x) {
        if (isNaN(a.value) || isNaN(b.value)) {
            s.innerText = "输入错误！";
            return;
        }
        switch (x) {
            case 1:
                s.innerText=a.value*1+b.value*1;
                break;
            case 2:
                s.innerText=a.value-b.value;
                break;
            case 3:
                s.innerText=a.value*b.value;
                break;
            case 4:
                s.innerText=a.value/b.value;
                break;

        }
    }
    /*
    let v=document.querySelector("input[type='button']");
    function f() {
        if (isNaN(a.value) || isNaN(b.value)) {
            s.innerText = "输入错误！";
            return;
        }
        switch (v.value) {
            case "加":
                s.innerText=a.value*1+b.value*1;
                break;
            case "减":
                s.innerText=a.value-b.value;
                break;
            case "乘":
                s.innerText=a.value*b.value;
                break;
            case "除":
                s.innerText=a.value/b.value;
        }
    }

     */

</script>
</body>
</html>